1. Field of the Invention
The present invention relates to a photovoltaic apparatus for directly converting light energy such as solar energy into electric energy.
2. Description of the Prior Art
In recent years, there has been extensive research on photovoltaic apparatus because light energy is unlimited and clean. A photovoltaic apparatus of amorphous silicon type has the advantage of requiring low manufacturing energy and being easy to manufacture.
Photovoltaic apparatus of amorphous silicon is classified into one employing a light shielding substrate and one employing a light transmitting substrate.
FIG. 1 shows an example of the former. This apparatus employs a light shielding substrate 100 on which an insulating layer 101, metal electrodes 102, amorphous or microcrystal semiconductive layers 103 and transparent electrodes 104 are formed in this order.
FIG. 2 shows an example of the latter proposed in Japanese Patent Publication No. 60-41878. This apparatus employs a light transmitting substrate 110 on a rear surface of which transparent electrodes 111, amorphous or microcrystal semiconductive layers 112 and electrodes 113 are formed in this order. Each electrode 113 comprises a plurality of metal layers or ITO-silver layers.
In the apparatus of FIG. 1, since the amorphous or microcrystal semiconductive layers 103 are in contact with the metal electrodes 102, compounds may be generated on the interfaces therebetween. This causes the reflectance of the metal electrodes 102 to be lowered to about 80% or less. In addition, since the light is not reflected between the metal electrodes 102, the amount of light reflected on the metal electrodes 102 and incident into the amorphous or microcrystal semiconductive layers 103 is reduced. As is apparent from the above, this type of apparatus has the problem that photoelectric conversion efficiency is lowered.
On the other hand, in the apparatus of FIG. 2, since the connecting portions 114 for connecting the transparent electrodes 111 are formed of the same material as the metal electrodes 113, the upper ends 114a of the connecting portions 114 reflect the light. That is, the amount of light incident the metal electrodes 113 is reduced due to the connecting portions 114. In addition, as in the apparatus of FIG. 1, the light is not reflected at portions 115 between the metal electrodes 113, whereby the amount of light reflected at the metal electrodes 113 and incident the layers 112 is reduced. Thus, this type of apparatus also has the same problem as the apparatus of FIG. 1.